Republicans in Congress say they are united in their determination to repeal and replace Obamacare.

But they appear to have different views over whether it’s OK to repeal the law before crafting a replacement, or whether the two steps must take place at once.

On Tuesday, a key House Republican talked up the former approach while a key Senate Republican seemed more inclined to support the latter.

Wiping away the Affordable Care Act has been a top GOP priority since President Barack Obama signed the law in 2010. Come January, Republicans will have control of both houses of Congress as well as the White House giving them the political power to realize their goal.

But today, more than 20 million people depend upon the law for insurance, and the number of uninsured Americans has fallen to historic lows. That’s a big reason why Republicans, including President-elect Donald Trump, have always insisted that they wouldn’t simply yank away coverage that they’d put a new, better system in its place.

The question is how to go about that. It’s complicated, because Republicans will have a narrow majority in the Senate, well short of the 60 votes they would need to break a likely Democratic filibuster.

Republicans could pass a bill repealing most of the law, including its all-important funding, using the budget “reconciliation” process a procedure for certain fiscal measures that would not be susceptible to the filibuster. But a replacement bill would require changing regulatory authority, among other things and that would almost certainly have to go through regular order, where the Democratic minority could block legislation (unless Republicans decide to eliminate the filibuster altogether).

Some Republicans have already floated the idea of using reconciliation to pass repeal, then postponing the effective date for a year or two so that they would have time to craft a replacement. They say this strategy, which has come to be known as “repeal and delay,” would avoid disruption for people who currently rely on Obamacare for their insurance.

House Majority Leader Kevin McCarthy (R-Calif.) endorsed this strategy during a pen-and-pad session with reporters on Tuesday.

“There will be a transition period,” McCarthy said, adding that the political incentives would motivate everybody, including Democrats, to bargain in good faith over a replacement. “You have a date certain that something is going away, a time period there, you now you need to have something there.”

In response to a question about whether replacement would pass in such a scenario, McCarthy imagined what reporters could ask recalcitrant lawmakers unwilling to sit down and bargain: “You know this is going away five months from now, and you’re going to avoid it? Here’s a time to get it done, but when that date came, and you did nothing? … You want to play politics?”

But on the other side of the Capitol building, Sen. Lamar Alexander (R-Tenn.) was openly skeptical of such an approach.

Alexander, chairman of the Health, Education, Labor, and Pensions Committee, had said previously that he thought fully repealing and replacing Obamacare would require bipartisan consensus and could take years.

When a reporter asked Alexander on Tuesday whether he was worried about talk of repealing Obamacare in January, once the new Congress begins, he said: “It would only concern me if [we] hadn’t figured out a way to replace it. I’m almost certain we’ll start almost immediately to replace Obamacare and repeal it. But in the end, they’ll finally have to be done at the same time.”

Alexander may have some company, even on the House side. Rep. Dennis Ross (R-Fla.), a senior deputy majority whip, told Bloomberg Politics: “In my view, the repeal is not nearly as important as replacement.”

“To just say, ‘Repeal everything, and the mandates, without a replacement,’ then what?” Ross went on to ask. “I don’t think we can do a repeal without a replacement. People are already in the system.”

One reason Republicans are worried about repeal-and-delay may be practical. If repeal passes, insurers could start pulling out of markets immediately, regardless of any transitional period leaving millions of people with no coverage.

Sylvia Burwell, the outgoing secretary of Health and Human Services, has warned that such a strategy could create chaos. Independent experts like Larry Levitt, senior vice president of the Henry J. Kaiser Family Foundation, agree.

“Any significant delay between repeal of the ACA and clarity over what will replace it would likely lead insurers to exit the marketplaces in droves,” Levitt told The Huffington Post. “Insurers have been sticking it out for the promise of future profits, but if the future becomes uncertain, they’ll have little reason to stay in the market.”

Insurers might be particularly spooked about the prospect of only people with serious, expensive-to-treat health problems staying in the market. “It would be like a game of musical chairs,” Levitt said. “When the music stops, no insurer wants to be the only one left in the market with all of the sick people.”

And then there’s the question of whether Republicans could even come together on a replacement bill.

House Republicans spent six years arguing over how to replace Obamacare before finally agreeing on a set of principles. Even now, they’ve not united behind a detailed plan in which the real-world trade-offs how much money to spend, how many people to cover, how many benefits to include, and so on are apparent. Senate Republicans haven’t even gotten that far.

How this all plays out over the next few months and years is impossible to say right now in no small part because Trump’s own intentions remain unclear. As a candidate, he repeatedly and vocally promised to repeal the health care law. But he also insisted he would replace it with something better and that he would not let people “die in the streets.”